If You Want to Help the Environment, Sometimes It's Better to Fly Than Drive

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The prospect of flight can make some environmentally conscious travelers a bit queasy.

A commercial jetliner can burn thousands of gallons of fuel on a single trip, leaving a big carbon footprint behind. Meanwhile, cars are getting more efficient, so maybe it would be better to drive.

Maybe — or maybe not.

While jets still burn a lot of fuel, today's average commercial airliner is far more efficient than the typical car for many trips, according to a new study from the University of Michigan's Transportation Research Institute.

In fact, Michigan researcher Michael Sivak found that the relative efficiencies of driving and flying have flipped since 1970.

"The main finding of that study was that, while flying domestically in the US used to be much more energy intensive than driving, that is no longer the case," Sivak wrote.

That gap has only widened in the past two years, even though automotive fuel efficiency is going up, he added. An airline workhorse like a Boeing 737 might burn 1,000 gallons of fuel on a 500-mile flight, but it'll carry 100 or more people in the process. A car might get 30 miles per gallon or more, but it's only hauling one person to work.

As a result, Sivak found cars used about double the amount of energy per passenger-mile than a US domestic flight. The most efficient form of transportation was passenger rail, which used barely a third of the energy as cars.

US Environmental Protection Agency figures show transportation makes up about 28 percent of US greenhouse gas emissions, adding the equivalent of about 1.8 billion tons of carbon dioxide to the atmosphere every year. More than 60 percent of that comes from the roughly 250 million cars and light trucks on American roads, while aviation makes up about 8 percent.

Of course, your mileage may vary. Dan Rutherford, the aviation program director for The International Council on Clean Transportation, said the Michigan study involves "a little bit of an apples-to-oranges comparison."

"You don't fly a plane to pick up a gallon of milk, and you don't take an urban bus from LA to New York City," Rutherford told VICE News. But if you're trying to figure out the most environmentally friendly way to make your holiday visit with relatives in Phoenix or Little Rock or Portland, "then you do a different comparison."

"When you make that comparison, planes get less efficient because they're flying over shorter routes," said Rutherford, whose organization ranks the relative fuel efficiencies of airlines. "They're burning more fuel on landing and takeoff, and they're also smaller on average, which impacts their efficiency. And cars and buses get significantly more fuel-efficient, because you're driving them on the highway and putting a lot more people in them."

Related: As the world prospers, more people are getting air conditioning — and that's really bad for the climate

But Rutherford said improved designs and smarter operation has increased the efficiency of jetliners by about 45 percent since the 1970s, while the automotive trend "has been somewhat in the opposite direction."

"As we've gotten richer, as we've suburbanized, the average efficiency of cars has gone down over time," he said. The introduction of federal fuel efficiency standards in the 1970s produced an improvement, "and then flatlined for a long time."

Sivak found the average drive is about 9 miles, while the typical domestic flight is nearly 900. When it comes to shorter trips, the comparison looks better for cars: Fuel mileage goes up in highway driving, while jetliners burn a bigger share of fuel on takeoff and landing.

Meanwhile, one of the biggest drivers of the improvements for airlines is one of the things that makes passengers nuts. Deron Lovaas, a senior adviser to the Natural Resources Defense Council's Urban Solutions program, told VICE News he has made four cross-country flights so far this year. "Every plane I flew on was full," he said.

"The fact that planes are increasingly full, or nearly full, means much more efficient use of every gallon of fuel that's used," said Lovaas.

"I don't think people are going to be substituting one for the other. They serve different purposes," he said. But he said the Michigan study shows "that at least compared to driving, it's not so bad."

Related: The Obama administration just sent the auto industry a tough message about climate change

Follow Matt Smith on Twitter: @mattsmithatl

Image via Flickr